Corn is the most important crop grown in the United States and is the second largest crop grown in the world. A corn plant begins life as a seed, also known as a kernel. The kernel has three main parts: (1) an embryo, or germ, that develops into the plant; (2) an endosperm consisting primarily of starch that is used for energy by the embryo; and (3) a seed coat. After planting in the ground, the kernel develops into a seedling and then a mature plant. A mature corn plant consists of roots, an upright stalk, leaves, one or more ears (each consisting of hundreds of kernels on a cob), and a tassel. A typical corn plant grows to a height of about three meters and has a life span of about five months.
A corn plant reproduces sexually. Male sex cells from pollen released by the tassel unite with female sex cells on the cob. Most of the pollen falls on other plants, but some self-pollination typically occurs. The fertilized sex cells develop into the kernels on the cob. Unfertilized female sex cells result in empty spots on the cob.
Most corn grown in the United States is of a genetic type known as hybrid corn. Hybrid corn is produced by a lengthy breeding process which begins by growing selected corn plants under conditions where inbreeding occurs, i.e., the selected plants are fertilized only by other plants in the same selected group. The inbreeding process is continued for several generations until all the plants in the group have similar genetic compositions. The next step in the process is to cross two inbred varieties. This is accomplished by planting the two varieties in close proximity to each other and removing the tassels of one of the varieties. The plants with the removed tassels are fertilized by the other variety of plants. The resulting kernels from these plants are known as single-cross corn hybrids and have a genetic composition which is a combination of the two inbred varieties.
Corn kernels are a common food for both animals and humans. Corn kernels are separated from other portions of the corn plant during the harvesting process and typically represent approximately fifty percent of the total dry mass of the corn plant. The non-kernel portion of the corn plant represents little nutritional value to humans and similar simple-stomached animals, because it is high in fiber and other components that cannot be effectively broken down by their digestive systems. Ruminant animals, such as cattle, have complex compartmentalized stomachs that allow for the breakdown and nutritional utilization of certain plant fiber materials. As a result, the non-kernel portion of the corn plant can be used as a source of nutrients for ruminants.
Corn silage is one form by which the total corn plant has historically been utilized as a source of nutrients for ruminant livestock. The process of making corn silage, known as ensiling, begins with the harvesting of the plant at a time when the combination of yield and overall nutrient value of the whole plant is at its maximum. This is typically associated with a plant that is high in moisture and thus subject to rapid decay unless somehow stabilized. The ensiling process makes use of a natural fermentative process that results in a lowering of the pH, i.e., an increase in acidity, and removal of oxygen from the silage mass to the point that it becomes resistant to spoilage. When properly ensiled, stored, and handled, corn silage can be fed over a period of several months after harvest.
The ensiling process is a complex interaction of many factors and phenomena. First, there is a series of issues associated with the physical and chemical characteristics of the corn plant utilized. In addition, the ensiling process itself requires the proper integration of several other steps and phenomena, all of which impact the quality of the final product.
A considerable amount of variation and interaction exists relative to the factors associated with silage production and its subsequent nutritional and related economic value. As a result, a considerable amount of research effort has gone into understanding and identifying ways to improve silage quality. Much of past work has focused on evaluations of a finished, ensiled product.
The economic value of corn silage is related to its ability to serve as a source of nutrients, which in turn is related to its compositional characteristics. The compositional characteristics of corn silage are primarily a function of the compositional characteristics of the corn plant and the microbial activities associated with the ensiling process. To maximize the extraction of value from differences in corn plant compositions, the composition must be accurately described. A major impediment to the accurate compositional evaluation of corn silage has been the nature of the corn plant itself. A corn plant is an organism that is made up of many highly specialized components. These specialized components display both chemical and physical differences. Obvious to even a casual observer are the physical differences between various plant parts, such as the stalk, leaves, grain, cob, etc. This diversity of chemical and physical characteristics presents a number of challenges relative to the obtaining of truly representative samples for compositional analysis. These differences make it difficult to obtain a high degree of sample homogeneity. Sample homogeneity is especially critical in light of the relatively small quantities of sample utilized as a part of most commercially applied analytical procedures. A further confounding factor is the effect that environment has on the expression of plant characteristics. Even within a given field, i.e., population, of corn, different microenvironments may exist. If not properly addressed, this can further confound such evaluations.
Describing the characteristics of a large population, such as a field of corn, through the use of samples requires that the samples be truly representative of the aggregate population. In the case of a population of whole corn plants, the above factors represent a significant challenge to being able to obtain samples which are truly representative of the aggregate population. This issue is further magnified when considered in the context of the small quantities of samples typically utilized for laboratory analysis. Thus, the ability to obtain homogeneous samples that truly represent the above-root corn plant population from which they are obtained is critical to the compositional evaluation of whole corn plant populations. Without the ability to consistently obtain, process, and analyze truly representative samples of aggregate whole corn plants, a considerable amount of sampling error is introduced into the evaluation process. The net effect is that true advantages and improvements in whole plant compositional traits are hidden by the gray area of sample variation. As a result, progress in identifying and capturing value from such differences is stifled. This aspect continues to represent a major challenge to those trying to identify compositional differences between populations of corn plants.
One approach to dealing with a large amount of inherent sample variation is to incorporate the use of more samples to better describe the population the samples are supposed to represent. For example, one study of corn plants used twenty whole plants and forty ears. C. Philippeau and B. Michalet-Doreau, “Influence of Genotype and Ensiling of Corn Grain on In Situ Degradation of Starch in the Rumen,” Journal of Dairy Science, Vol. 81, No. 8, 1998, pp. 2178-2184. Because the cost of this type of research is directly related to the expenses associated with sample procurement, processing, and analysis, addressing large inherent sample variation through increased sample numbers becomes a direct research cost issue. Accordingly, a demand exists for a process that improves the ability to obtain and analyze truly representative samples from populations of whole corn plants. Such a process would benefit the silage evaluation process by providing for both greater accuracy and precision of results while reducing the associated expenses.